The present invention relates to the control of an electromechanical actuator assembly including an actuating member moved by energization of an associated electrical coil, and particularly to techniques for identifying a position of the actuating member relative to the coil by measuring a parameter representative of inductance attributable to a position of the actuating member. The invention has intended use relating to the control of a fuel, such as a gas flow to a burner, when the fuel is communicated to the burner through an electromagnetically operated valve. The invention is most applicable to techniques for remotely controlling an electrically operated proportional valve to provide closed loop valve position control, but is also applicable to any type of electromechanical actuator having a varying parameter resulting from actuator movement.
A wide variety of sensing devices for detecting position of an actuating member in an electromechanical actuator assembly are known in the art. Most of these devices employ supplemental devices on the electromechanical actuator assembly to monitor relative positions of the working elements of the assembly. For example, numerous types of proximity sensors, limit switches and the like to detect actuator movement have been employed. In particular, common present day actuator position sensing devices will employ a magnetic sensor such as a Hall or magneto-resistive sensor located inside the valve to measure position. Another common system presently used is to attach a potentiometer to the moving member at an external location. Such various forms and types of sensing systems have enjoyed varying degrees of success, but they all have been found to have limits on their economic and practical value. In particular, all involve supplemental internal or externally mounted position transducers, which can significantly increase the complexity of the system and its costs. Particularly, when considered in the context of a gas burner, it is desirable that the control system have the ability to control the level of heat accurately and cost-effectively.
The gas range of the future will have more electronics than ever. One area where electronics is likely to come into play is in control of the valve itself. Such control will allow for features such as temperature versus time profiles, time programmed cooking, and locating the operation knob away from a hot burner location. Closed loop position control of an electromagnetic valve will allow the set position to be accurately maintained even in the presence of varying supply pressures. It will also provide greater safety as the actual valve position is always monitored.
Another safety concern for modulating gas valve assemblies is hang-up of the valve member. Most valve members are spring-biased to force the member closed so that when power to the actuating coil is cutoff, the valve member will close and shutoff gas flow to the burner. In those circumstances where a spring does not or cannot force the valve member closed, the gas flow is left running to the burner. A piece of dirt on the valve seat is an example of what could cause hang-up.
The present invention contemplates a new and improved electromechanical actuator control scheme comprising a position sensing circuit which overcomes the above-referred to problems and others to provide a new control system and method which is simple in design, economical to manufacture and readily adaptable to a plurality of electromechanical actuators, including flow control valves.